Communities throughout the United States are requiring a larger percentage of all municipal waste to be recycled in order to minimize landfill disposal of municipal waste. Recycling of municipal waste, in most circumstances, requires separating the waste stream into its constituent parts. One way to achieve this is to require the producer of the waste to separate the material into various categories, for instance, plastic, glass, paper and aluminum cans and foil. With many motivated citizens participating, this can be a highly effective way of separating waste. However, in many circumstances, it will not prove cost effective. The collection of multiple receptacles filled with differing wastes can significantly increase the cost of collection which is a major component in the cost of disposing of municipal wastes. In many circumstances, it will not prove possible to pre-separate the trash before collection with the result that undifferentiated trash must be processed and separated if a major fraction of the material is to be recycled.
Numerous material separation processes borrowed from the scrap industry or the mining industry may be applied to municipal wastes. For instance, magnetic separation of ferrous materials may be readily applied to a stream of municipal wastes moving on a conveyor belt. However, often the separation techniques require that the material be comminuted or crushed to a uniform size in order for the separation techniques to be applied.
While separation of a granulized waste stream may facilitate the recovery of some constituents, such as glass, by sorting the material on the basis of density, such processes often degrade the quality of the recovered material for further use. In the case of glass, for example, the more valuable clear glass becomes commingled with the less valuable dark brown and green glasses. Similarly, once plastic containers have been ground, it is no longer as practical to separate the plastic in the waste stream into its various types, thus substantially reducing the value of the recovered materials.
A solution to the problem associated with particularizing the waste is to separate the waste before the constituents are ground up for reprocessing. Unfortunately, this has usually resulted in the necessity of utilizing garbage picking lines where individual laborers remove the different constituents of the waste as it flows along a conveyor. Picking lines are labor-intensive and thus expensive. Cost is even higher if the waste is contaminated with hazardous material such as medical wastes, diapers, and various fibers or toxic materials. Presence of such hazardous materials necessitates the use of safety equipment which is not only expensive, but can reduce the laborers' efficiency in separating materials from the waste stream.
A typical waste stream is composed of paper, plastic, glass, non-ferrous metals, and organic wastes. These materials are normally visually distinguishable and thus can be separated with manual labor.
What is needed is a method and apparatus which can separate the various components of municipal waste automatically in a way that is analogous to the manual labor used on garbage picking lines.